Method and associated instrumentation for installation of spinal dynamic stabilization system

ABSTRACT

In one embodiment, a spinal stabilization apparatus includes a vertebral anchor having a head portion and a bone attachment portion. An elongate, flexible guide is removably coupled to the head portion of the vertebral anchor and has a channel extending longitudinally thereof and communicating with a slot in the head portion of the anchor. An elongate cord may be received within the channel to facilitate inserting and securing a spacer between pairs of anchors installed into adjacent vertebrae of a person&#39;s spine.

TECHNICAL FIELD

This invention relates generally to spinal support devices, and moreparticularly to methods and devices that facilitate installing animplantable system for providing dynamic stability of a person's spine.

BACKGROUND OF THE INVENTION

The treatment of acute and chronic spinal instabilities or deformitiesof the thoracic, lumbar, and sacral spine has traditionally involved theimplantation of rigid rods to secure the vertebrae of a patient. Morerecently, flexible materials have been utilized in connection withsecuring elements, such as pedicle screws, to provide a dynamicstabilization of the spine. Such dynamic stabilization systems typicallyinclude a flexible spacer positioned between pedicle screws installed inadjacent vertebrae of person's spine. Once the spacer is positionedbetween the pedicle screws, a flexible cord is threaded through eyeletsformed in the pedicle screws and an aperture through the spacer. Theflexible cord retains the spacer between the pedicle screws whilecooperating with the spacer to permit mobility of the spine. Traditionalimplantation of such dynamic stabilization systems may requirerelatively large surgical sites to permit threading the cord through thescrews and spacer once the spacer has been positioned between thescrews.

While some dynamic stabilization systems have been proposed forpermitting the top loading of a spacer and cord between pedicle screws,these systems also require added instrumentation and procedures todistract the pedicle screws for placement of the spacer.

A need therefore exists for a spinal dynamic stabilization system andassociated installation tools and techniques that overcome these andother drawbacks of the prior art.

SUMMARY OF THE INVENTION

This invention overcomes the foregoing and other shortcomings anddrawbacks of spinal stabilization systems heretofore known for use insuitable various commercial and industrial environments. While variousembodiments will be described herein, the invention is not limited tothese embodiments. On the contrary, the invention includes allalternatives, modifications and equivalents as may be included withinthe spirit and scope of this invention.

In one embodiment, a system for stabilizing a patient's spine includes apair of vertebral anchors adapted to be anchored to first and secondvertebrae, respectively. Each vertebral anchor has an upwardly openchannel. A connecting element that may be in the form of a flexible cordextends between the vertebral anchors and is seated in the channels. Anannular spacer is positioned between the channels of the vertebralanchors with the connecting element passing there through. A pair offasteners is each mated with the one of the channels of the vertebralanchors to secure the connecting element thereto. A pair of accessmembers in the form of sleeves is mounted on the vertebral anchors andeach sleeve has a cannula to provide percutaneous access to thevertebral anchor when mounted thereon.

A slot in each of the sleeves is in communication with the associatedchannel when mounted on the vertebral anchor. The system includes onetool having a tubular member with a cannula extending there through andconfigured to fit over one of the sleeves when mounted on the associatedvertebral anchor. The tool is used by the surgeon to advance theconnecting member along the slot and into the channel of one of thevertebral anchors and to position the spacer between the vertebralanchors. In alternative embodiments, the tool may have an arcuate flangeon its distal end to cradle the spacer for distraction during insertionbetween the vertebral anchors.

The system may include another tool also having a tubular member with acannula extending there through and configured to fit over one of thesleeves when mounted on the associated vertebral anchor. This tool isadapted to advance the connecting member along the slot and into thechannel of the vertebral anchors. This tool may include a mating featureproximate the distal end and complementary to a mating feature on eitherthe vertebral anchor or the sleeve to thereby couple the tool thereto.The complementary mating features may include a recess on the distal endof the tool, a recess on the head of the pedicle screw, an outwardlydirected protrusion proximate a distal end of the sleeve, and aninwardly directed protrusion proximate the distal end of the sleeve. Therecesses are configured to mate with the protrusions to releasablysecure the tool to the pedicle screw and allow the surgeon to use thetool to screw the pedicle screws into the vertebrae.

Other embodiments of this invention involve the installation proceduresfor a spinal stabilization construct and include installing thevertebral anchors onto the vertebrae and mounting access members, whichin one embodiment are sleeves, onto the vertebral anchors. Each sleevehas a cannula to provide percutaneous access to the channel of therespective vertebral anchor. The connecting element is inserted througha slot in one of the sleeves and is advanced from the slot into thechannel in the associated vertebral anchor. The connecting element issecured to the channel of the vertebral anchor with a fastener and anannular spacer is positioned on the connecting element adjacent thevertebral anchor.

The connecting element is inserted through a slot in the other sleeveand advanced into the channel in the second vertebral anchor. The spacerdistracts against the first vertebral anchor and positions the spacerbetween the vertebral anchors. The connecting element is secured to thechannel of the second vertebral anchor with a second fastener. Theconnecting element may be a flexible cord that is tensioned between thevertebral anchors. The respective fasteners may be passed through thesleeves percutaneously to the respective channels in conjunction withthe tensioning of the cord or connecting element.

These and other features, objects and advantages of the invention willbecome more readily apparent to those skilled in the art in view of thefollowing detailed description, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with the general description of the invention given above, andthe detailed description given below, serve to explain the principles ofthe invention.

FIG. 1 is a perspective view of a vertebral anchor in the form of apedicle screw and an associated fastener in the form of a set screwaccording to one aspect of this invention;

FIG. 2 is a perspective view of the vertebral anchor of FIG. 1 beingcoupled to an access sleeve according to one aspect of this invention;

FIG. 3 is a perspective view of the components of FIG. 2 being coupledto a tool according to another aspect of this invention;

FIG. 4 is a perspective view of the components of FIG. 3 being used toscrew a first vertebral anchor into a vertebrae of a patient;

FIG. 5 is a perspective view of a connecting element of a dynamicstabilization system being installed on the first vertebral anchor ofFIG. 4;

FIG. 6 is a perspective view of the components of the dynamicstabilization system being installed relative to a pair of vertebralanchors installed on respective vertebrae of the patient; and

FIG. 7 is a perspective view of the connecting element of the dynamicstabilization system being tensioned between the vertebral anchors andthe anchors being distracted during the tensioning process.

DETAILED DESCRIPTION

FIGS. 1-2 and 6-7 depict some of the components of one embodiment of aspinal stabilization system 10 according to this invention.Specifically, vertebral anchors 12 are adapted to be installed intoadjacent vertebrae 14, 16 of the spine using removable access members 18inserted through an incision formed through the patient's skin. Theincision may be sized for minimally invasive percutaneous or retractorbased techniques or may be used in open procedures. In the embodimentshown, at least two anchors 12, shown here in the form of pediclescrews, are fixedly installed into the pedicle area of adjacentvertebrae 14, 16 and a flexible spacer 20 is disposed there between tocontrol motion of the spine, while otherwise leaving the spinal segmentmobile. Alternatively, the two anchors can be placed in a patient incombination with a fusion device located between the vertebral bodies.

The spacer 20 and pedicle screws 12 are coupled together by a connectingelement 22 which in one embodiment is a flexible member coupled to orpassed through the spacer 20 and secured to the heads 24 of the screws12. Such spacers 20 and flexible members 22 may be similar to those usedin the Dynesys® Dynamic Stabilization System available from Zimmer Spineof Minneapolis, Minn. In one embodiment, the spacer 20 may be formedfrom polycarbonate urethane and the flexible member 22 is a cord thatmay be formed from polyethylene-terephthalate, although it will berecognized that various other materials suitable for implantation withinthe human body and for providing stabilization of the spine whilemaintaining flexibility may be used.

In one embodiment, the anchor 12 is a pedicle screw having a threadedshank 26 configured to be screwed into the pedicle area of a vertebra14, 16. The head 24 of the screw is configured to receive and secure theflexible member 22. In the embodiment shown, the head 24 includes anupwardly open channel 28 formed between upwardly directed arms 30 andextending generally transverse to the longitudinal axis of the shank 26and having an open end opposite the shank 26 for receiving the flexiblemember 22 into the channel 28 of the head 24 in a top loading fashion.Accordingly, the channel 28 alleviates the need to thread the flexiblemember 22 through an eyelet of the head 24 of the anchor 12 after theanchor 12 has been installed into the vertebral body 14, 16 of apatient's spine. The head 24 may have a pair of spaced, generally flatface 33 for juxtaposition to the spacer 20.

In this embodiment, the head 24 of the pedicle screw 12 has receivingchannels, such as recesses 32, provided on oppositely disposed sides ofthe arms 30 of the head 24 to facilitate screwing the anchor 12 into avertebra 14, 16 of a patient's spine using a tool as described laterherein. In one embodiment, the pedicle screw 12 is formed from atitanium alloy, but it will be recognized that various other materialssuitable for implantation within the human body and having sufficientstrength to be securely attached to the bone and to secure the flexiblemember 22 may be used. While a uniaxial pedicle screw is shown anddescribed herein, it will be recognized that the anchor 12 mayalternatively comprise a hook, a polyaxial pedicle screw, or variousother structure suitable to be secured to a vertebral body.

An elongate access member 18 is removably secured to the head 24 of thepedicle screw 12 and is formed substantially from a resilient, flexiblematerial that permits deformation or bending of the access member 18along its length without transmitting significant force to the pediclescrew 12. For example, the access member 18 may be formed from polymericmaterial such as nylon, polyethylene, polyurethane, or various otherpolymeric materials that are biocompatible and provide sufficientflexibility to permit the guides to bend in flexure along their lengthwithout transmitting significant force to the pedicle screw 12. In otherexemplary embodiments, the access members 18 may be configured as arigid or a composite structure, comprising a portion formed from asubstantially rigid material and a portion comprising a flexiblematerial or wholly of a rigid material.

In the embodiment shown in FIG. 2, the access member 18 includes a pairof diametrically opposed, longitudinal slots 34 extending from a first,distal end 36 toward a second, proximal end 38 of the access member 18.Each slot 34 has an opening 40 at the first end 36 that is shaped tomate with the head 24 of the pedicle screw 12 such that the slot 34communicates with the channel 28 formed in the head 24 of the pediclescrew 12. In this arrangement, the longitudinally extending slot 34 maybe used to guide the flexible member 22 from the slots 34 of the accessmember 18, along its length, and into the channel 28 formed in the head24 of the pedicle screw 12.

In one embodiment, the access member 18 includes mating tabs 42 to matewith the receiving channels or recesses 32 on the head 24 of the pediclescrew 12. In the exemplary embodiment shown, the mating tabs 42 areinwardly direct protrusions. Mating surfaces between the pedicle screwand the access member 18 are configured to provide a mechanicalinterlock that is sufficient to withstand forces applied to the accessmember 18 during installation of the pedicle screws 12 into thevertebrae 14, 16 and installation of the spacer 20 between adjacentpedicle screws 12. However, the access members 18 may be removed fromthe heads 24 of the pedicle screws 12, for example, by application of anappropriate force or by manipulating the access member 18 relative tothe pedicle screw 12, to cause the mating tabs 42 on the access member18 to dislodge from the recesses 32 on the head 24 of the pedicle screw12. The access member 18 may be formed in a molding process in the formof a sleeve having a longitudinally extending cannula 44, and maythereafter be joined to the head 24 of the pedicle screw 12 bymechanically interlocking the sleeve 18 onto the head 24 the pediclescrew 12 with the mating tabs 42 and receiving channels like recesses32.

With continued reference to FIGS. 1-2, the sleeve 18 includes anaperture 48 proximate the second end 38 for receiving various componentsincluding a fastener 50, such as a set screw, for securing the flexiblemember 22 to the head 24 of the pedicle screw 12, as will be describedmore fully below. The aperture 48 leads to the cannula 44 of the accessmember 18 to provide percutaneous access to the head 24 of the pediclescrew 12.

Longitudinally extending and laterally oriented threads 52 are formed onthe inwardly facing surfaces of the arms 30 in the channel 28 of thehead 24. The threads 52 are sized for engagement with the fastener 50when it is desired to secure the flexible member 22 to the head 24 ofthe pedicle screw 12. In one embodiment, a driver 54 (FIG. 7) or othertool suitable for engaging a socket 56 in a top face of the fastener, orset screw, 50 may be inserted through the cannula 44.

While the fastener 50 has been shown and described herein as comprisinga set screw, it will be recognized that various other types of securingmembers may alternatively be used to secure the flexible member 22 tothe head 24 of the anchor 12. Likewise, the sleeve 18 may be configuredto accommodate these various other types of fasteners and topercutaneously provide access for them to the anchor 12.

Referring now to FIG. 3, use of a tool 60 to install components of thespinal stabilization system 10 to the vertebrae 14, 16 of a spine willnow be described. Vertebral anchor 12 and sleeve 18 mated together havebeen inserted through a minimally invasive incision formed in apatient's skin to be threadably secured into the pedicle areas of avertebrae 14, 16. The tool 60 in one embodiment as shown includes atubular member 62 extending longitudinally and defines a central cannula64 extending from a distal end 66 of the tool 60. The tool 60 includes ahandle 68 at the proximal end 70 of the tubular member 62 and the handle68 and tubular member 62 in combination form a generally T-shapedconfiguration according to one embodiment of the tool 60. In oneembodiment, the T-shaped handle configuration of handle 68 can beincorporated into the sleeve 18. The proximal end 70 of the cannula 64in the tubular member 62 is accessed through a port 72 in the handle 68as shown in FIGS. 3 and 4. The port 72 is sized to receive a fastener50. The handle 68 provides a convenient grip for a surgeon to grasp thetool 60 for manipulation during installation of the spinal stabilizationsystem 10. The distal end 66 of the tubular member 62 includes a pair ofdiametrically opposed fingers 74 projecting downwardly. Tool receivingchannels, such as recesses 76, are formed on an inner face of eachfinger 74 and extends longitudinally toward the body portion of thetubular member 62. The cannula 64 and tubular member 62 are sized andconfigured to fit over the access member 18 and pedicle screw 12combination as shown in FIG. 3.

Referring to FIG. 4, with the tool 60 installed onto and over the accessmember 18 and pedicle screw 12 in a generally telescopic arrangement,the recesses 76 at the distal end 66 of the tubular member 62 mate withoutwardly directed tool mating tabs 78 on the distal end of the accessmember 18. As a result, the tool 60 is mated with the vertebral anchor12 and access member 18. The mating interaction of the mating tabs 42,78 and recesses 32, 76 allow the T-shaped tool 60 to drive the pediclescrew 12 as well as act as an anti-torque instrument. The surgeonrotates the tool 60 mated with the vertebral anchor 12 and access member18 to screw the vertebral anchor 12 into the vertebrae 14, 16. The tool60 can then be uncoupled from the access member 18 by dislodging thetool mating tabs 78 from the recess 76, thereby leaving the accessmember 18 mounted on the pedicle screw 12 installed on the vertebrae 14,16.

The above-described description of the installation of the pedicle screw12 may be performed on each of the pedicle screws 12 utilized in thestabilization system 10 as appropriate. In FIG. 5, the attachment of theconnecting member, such as the exemplary flexible member 22 in the formof a flexible cord, to one of the pedicle screws 12 is shown. Thepedicle screw 12 installed in the vertebrae 14 has the access member 18mounted thereto as shown in FIG. 5. A terminal end 22 a of theconnecting element 22 is inserted through the slots 34 of the accessmember 18 and this is likely performed at a portion of the slots 34 andaccess member 18 extending from the patient's body and above theincision. A forceps 80 having a pair of elongate handle members 82pivotally coupled together can be utilized to stabilize and maneuver theflexible member 22 in the access member slots 34. The forceps 80 includecooperating jaws 84, each of which has an arcuate portion 86 and adownwardly depending leg 88 with a notch go proximate the distal end ofthe leg 88 as shown in FIG. 5. In combination, the jaws 84 of theforceps 80 surround the access member 18 and the notches go clamp theend 22 a of the flexible member 22 projecting through the slot 34. Anyexcess portion of the flexible member 22 that overhangs the notches gomay be severed or trimmed as desired.

With the flexible member 22 clamped by the forceps 80 and projectingthrough the slots 34 in the access member 18 as shown in FIG. 5, theflexible member 22 may be passed through the slots 34 and down to thechannel 28 of the pedicle screw 12. The forceps 80 clamped onto theflexible member 22 and around the access member 18 may be utilized topush the flexible member 22 from the slots 34 and into the channel 28.Alternatively, the tubular member 62 of the tool 60 may be used incombination with the forceps 80 to advance the flexible member 22 fromthe slots 34 downwardly and into the upwardly open channel 28 of thepedicle screw 12 as shown in FIG. 5.

With the flexible member 22 seated in the channel 28 and secured thereinby the forceps 80, the fastener or set screw 50 may be percutaneouslyintroduced through the cannula 44 of the access member 18 for securingthe flexible member 22 to the pedicle screw 12. A driver 54 or similartool may be utilized to threadably secure the set screw 50 to the head24 of the pedicle screw 12 thereby securing the flexible member 22 tothe pedicle screw 12. The tubular member 62 and T-shaped tool 60 maycontinue to be mounted telescopically on the access member 18 andpedicle screw 12 or removed for easier access and installation of theset screw 50.

Referring to FIGS. 6 and 7, the adjacent pedicle screw 12 a has beenplaced in the associated vertebrae 14 with the procedure as previouslydescribed. The spacer 20 is then put over the flexible member 22 andslid into contact with the head 24 of the first pedicle screw 12 a asshown in FIG. 6. The tool 62 can be used to create distraction betweenthe vertebral anchors 12 a, 12 b to allow for easier placement of thespacer 20 between the vertebral anchors 12 a, 12 b. Alternatively, adistractive force can be generated by the placement of the spacer 20between the vertebral anchors 12 a, 12 b. As the tool 62 shown in FIG. 6is forced into engagement with the spacer 20, the spacer 20 thengenerates a force against the vertebral anchors 12 a, 12 b thus creatingdistraction of the vertebrae.

The flexible member 22 is then inserted through the slots 34 of theaccess member 18 on the second pedicle screw 12 b and a connectingelement guide tool 92 can be slid over the access member 18 on thesecond pedicle screw 12 b as shown in FIGS. 6 and 7. The cord guide tool92 is similar to the T-shaped tool 60 previously described in FIGS. 3and 4 with like reference numerals identifying similar features. Theflexible member guide tool 92 also includes at least one arcuate flange94 projecting generally perpendicularly from the axis of the tubularmember 62. The arcuate flange 94 is sized and configured to cradle aportion of the spacer 20 as the tool 92 is pushed downwardly over theaccess member 18. The arcuate flange 94 contacts the end of the spacer20 adjacent the second pedicle screw 12 b and downward pressure on thetool 92 forces the spacer 20 downwardly and into position between theadjacent pedicle screw heads 24. As the cord guide tool 92 slidesdownwardly over the access member 18, the arcuate flange 94 translatesthe spacer 20 downward and outward to create distraction by reacting tothe force of the flexible member guide tool 92 and pushing against theaccess member 18 on the second pedicle screw 12 b and the head 24 of thefirst pedicle screw 12 a. Simultaneously, the flexible member 22advances from the slots 34 of the access member 18 on the second pediclescrew 12 b and into the channel 28 of the head 24 of the second pediclescrew 12 b.

Advantageously, this invention utilizes the tools and spacer to createdistraction between the pedicle screw heads 24 and avoids threading theflexible member 22 through an eyelet in the head of the pedicle screwand any over distraction caused by the thickness of the flexible memberwhen pulled into position.

Once the spacer 20 is positioned between the pedicle screw heads 24 andthe flexible member 22 is seated in the channel 28 of the second pediclescrew 12 b, the flexible member 22 may be tensioned utilizing atensioning tool 96 as shown in FIG. 7. After the flexible member 22 isappropriately tensioned, the set screw 50 may be passed through the port70 in the handle 68 of the cord guide tool 92 and seated in the channel28 of the pedicle screw head 24. The driver 54 is then utilized throughthe cannula 64 of the tool 92 and the access member 18 to mate with theset screw 50 and rotate the set screw 50 into secure engagement in thechannel 28 and thereby clamp the tensioned flexible member 22. Thedriver 54, cord guide tool 92, access member 18 and tensioning tool 96may then be removed from the patient and the flexible member 22 trimmedto length. Alternatively, if a multi-level spinal dynamic stabilizationsystem 10 is to be installed, the process is repeated on subsequentvertebrae as appropriate and the incision closed to complete theinstallation.

While this invention has been illustrated by the description of one ormore embodiments thereof, and while the embodiments have been describedin considerable detail, they are not intended to restrict or in any waylimit the scope of the appended claims to such detail. Additionaladvantages and modifications will readily appear to those skilled in theart. The invention in its broader aspects is therefore not limited tothe specific details, representative apparatus and method andillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the scope or spirit ofthe general inventive concept

1. A method of installing a spinal stabilization construct comprisingthe steps of: installing first and second vertebral anchors onto firstand second vertebrae, respectively, each vertebral anchor having anupwardly open channel adapted to receive therein a flexible connectingelement extending between the first and second vertebrae; mounting firstand second access members onto the first and second vertebral anchors,respectively, each access member having a cannula to provide access tothe channel of the respective vertebral anchor; inserting the connectingelement through a slot in the first access member; advancing theflexible connecting element from the slot in the first access memberinto the channel in the first vertebral anchor; securing the flexibleconnecting element to the channel of the first vertebral anchor with afirst fastener; positioning a spacer on the connecting element adjacentthe first vertebral anchor; inserting the flexible connecting elementthrough a slot in the second access member; advancing the flexibleconnecting element from the slot in the second access member into thechannel in the second vertebral anchor; positioning the spacer betweenthe vertebral anchors; and securing the flexible connecting element tothe channel of the second vertebral anchor with a second fastener. 2.The method of claim 1 further comprising: tensioning the connectingelement after the first securing step and prior to the second securingstep.
 3. The method of claim 1 further comprising: distracting the firstand second vertebrae during placement of the spacer.
 4. The method ofclaim 2 wherein the second advancing step and the distracting step areperformed generally simultaneously.
 5. The method of claim 1 wherein thesecuring steps each further comprise: passing the respective fastenerthrough the respective access member percutaneously to the respectivechannel.
 6. The method of claim 1 wherein the steps are performedgenerally sequentially in the order recited in claim
 1. 7. The method ofclaim 1 wherein each vertebral anchor is a pedicle screw having athreaded shaft and a head, the channel being formed in the head, theinstalling step further comprising: coupling a tool to the head of eachof the pedicle screws; and screwing the shaft of each of the pediclescrews into the associated vertebrae.
 8. The method of claim 6 whereinthe tool has a tubular member with a cannula extending there through,the coupling step further comprising: inserting the respective accessmember mounted on the associated pedicle screw into the cannula of thetool.
 9. The method of claim 6 wherein the tool is utilized in the firstadvancing step.
 10. The method of claim 1 further comprising: trimmingthe flexible connecting element to length; and removing the accessmember from the vertebral anchors.
 11. The method of claim 2 wherein thesecond advancing step and the distracting step are performed with a toolhaving a tubular member with a cannula extending there through and adistal end, the method further comprising: inserting the cannula of thetool over the second access member mounted on the second vertebralanchor; and contacting at least one of the spacer and the flexibleconnecting element with the distal end of the tool.
 12. The method ofclaim 10 further comprising: cradling the spacer with an arcuate flangeon the distal end of the tool.
 13. A system for stabilizing a patient'sspine comprising: first and second vertebral anchors adapted to beanchored to first and second vertebrae, respectively, each vertebralanchor having an upwardly open channel; a flexible connecting elementadapted to be extend between the vertebral anchors and be seated in thechannels; a spacer adapted to be positioned between the channels of thevertebral anchors with the connecting element passing there through;first and second fasteners adapted to be mated with the channels of thefirst and second vertebral anchors, respectively, to secure the flexibleconnecting element thereto; first and second access members adapted tobe mounted on the first and second vertebral anchors, respectively, eachaccess member having a cannula to provide access to the vertebral anchorwhen mounted thereon; a slot in each of the access members incommunication with the associated channel when mounted on the vertebralanchor; and a first tool having a tubular member with a cannulaextending there through and configured to fit over one of the accessmembers when mounted on the associated vertebral anchor, the first toolbeing adapted to advance the flexible connecting member along the slotand into the channel of one of the vertebral anchors and to position thespacer between the vertebral anchors.
 14. The system of claim 13 furthercomprising: an arcuate flange on a distal end of the first tool adaptedto cradle the spacer for distraction between the vertebral anchors. 15.The system of claim 13 wherein the flexible connecting element is aflexible cord adapted to be tensioned between the vertebral anchors. 16.The system of claim 13 wherein each fastener is a set screw adapted tobe threadably mated with the vertebral anchor.
 17. The system of claim13 further comprising: a handle on the proximal end of the first tooladapted to be grasped by a surgeon for manipulation of the first tool.18. The system of claim 13 further comprising: a second tool having atubular member with a cannula extending there through and configured tofit over one of the access members when mounted on the associatedvertebral anchor, the second tool being adapted to advance the flexibleconnecting member along the slot and into the channel of one of thevertebral anchors.
 19. The system of claim 18 further comprising: ahandle on the proximal end of the second tool adapted to be grasped by asurgeon for manipulation of the second tool.
 20. The system of claim 19further comprising: complementary mating features proximate the distalend of the second tool and at least one of the vertebral anchors and theaccess members to thereby couple the second tool thereto.
 21. The systemof claim 20 wherein each vertebral anchor is a pedicle screw having athreaded shaft and a head, the channel being formed in the head, thesecond tool being adapted to screw the threaded shaft into the vertebraeupon rotation of the second tool when mated with the pedicle screw. 22.The system of claim 21 wherein the complementary mating features furthercomprise: a first recess on the distal end of the second tool; a secondrecess on the head of the pedicle screw; a first, outwardly directed,protrusion proximate a distal end of the access member; and a second,inwardly directed, protrusion proximate the distal end of the accessmember; wherein the first and second recesses are configured to matewith the first and second protrusions, respectively.
 23. The system ofclaim 13 wherein each access member further comprises: a sleeve with apair of longitudinal diametrically opposed slots.
 24. A system forstabilizing a patient's spine comprising: first and second pediclescrews each having a threaded shaft and a head with an upwardly openchannel, the first and second pedicle screws adapted to be anchored tofirst and second vertebrae, respectively; a flexible member adapted toextend between the pedicle screws and be seated in the channels; aspacer adapted to be positioned between the heads of the pedicle screwswith the cord passing there through; first and second set screws adaptedto be mated with the channels of the first and second pedicle screws,respectively, to secure the cord thereto; first and second sleevesadapted to be mounted on the first and second pedicle screws,respectively, each sleeve having a cannula to provide access to thepedicle screw when mounted thereon; a longitudinal slot in each of thesleeves in communication with the associated channel when mounted on thepedicle screw; a first tool having a tubular member with a cannulaextending there through and configured to fit over one of the sleeveswhen mounted on the associated pedicle screw, the first tool beingadapted to advance the flexible member along the slot and into thechannel of one of the pedicle screws and to position the spacer betweenthe pedicle screws; a second tool having a tubular member with a cannulaextending there through and configured to fit over one of the sleeveswhen mounted on the associated pedicle screw, the second tool beingadapted to advance the flexible member along the slot and into thechannel of one of the pedicle screws; and complementary mating featuresproximate the distal end of the second tool and at least one of thepedicle screws and the sleeves to thereby couple the second toolthereto, the second tool being adapted to screw the threaded shaft intothe vertebrae upon rotation of the second tool when mated with thepedicle screw.
 25. The system of claim 24 further comprising: an arcuateflange on a distal end of the first tool adapted to cradle the spacerfor distraction between the vertebral anchors.
 26. The system of claim24 wherein the complementary mating features further comprise: a firstrecess on the distal end of the second tool; a second recess on the headof the pedicle screw; a first, outwardly directed, protrusion proximatea distal end of the sleeve; and a second, inwardly directed, protrusionproximate the distal end of the sleeve; wherein the first and secondrecesses are configured to mate with the first and second protrusions,respectively.